1. Field of the Invention
The present invention generally relates to methods and systems for estimating, monitoring and managing road traffic. More specifically, the present invention relates to a method and system for determining traffic jams based on information derived from a cellular Public Land Mobile telephony Network (PLMN).
2. Description of the Related Art
The estimation, monitoring and management of road traffic are normally accomplished based on a count of the number of vehicles that pass through one or more points of the monitored network of roads.
Vehicles counting methods are essentially of two types: manual counting methods and automatic counting methods.
Manual vehicles counting methods provide that operators, staying at the prescribed monitoring points along the roads, visually count the passing vehicles.
Automatic vehicles counting methods provide for placing, on or within the road floor, detectors adapted to detect the passage of the vehicles. Different types of detectors can be used, the more common being:                rubber pipes closed at an end and connected to a membrane at the other end; the passage of a vehicle over the pipe creates a pressure thereinside that causes the membrane to flex, determining the increase of a vehicles counter;        metal coils through which an electric current is made to flow that produces an electromagnetic field; the passage of a vehicle alters the electromagnetic field, and this event is detected causing the increase of a vehicles counter;        television cameras connected to automatic image recognition systems adapted to count the number of transiting vehicles.        
The manual counting of the passing vehicles, requiring the continuous presence of people at the road sections to be monitored, is used only for time-limited monitoring campaigns.
On the contrary, automatic vehicles counting methods are used for monitoring the road traffic for relatively long periods of time; however, the deployment of the detectors on the roads network and their connection to a central data processing server is very expensive, especially in medium and large urban areas, which are the scenarios where the road traffic monitoring, estimation and management is more useful.
A known alternative to the above-described vehicles counting methods makes use of a certain number of vehicles (called “floating cars”) equipped with a GPS receiver which regularly transmit to a service center its position and speed, thereby allowing the service center to estimate the road traffic.
This method is as well very expensive, and its effectiveness is closely related to the number of circulating vehicles equipped with GPS receivers, i.e. to the number of floating cars; due to this, continuous monitoring of all the main roads of a certain area may not be possible.
In recent years, cellular PLMNs have also been used for the purposes of estimation, monitoring and management of the road traffic, thanks to the widespread presence of mobile phones among the population.
Systems that exploit cellular PLMNs for the estimation, monitoring and management of the road traffic varies according to the type of information on the position of the vehicles that they require for their operation.
For example, U.S. Pat. No. 5,465,289 discloses a system that makes use of sensors for monitoring communications going on in the cellular PLMN; number of calls placed, number of handovers performed, number of emergency calls are thus extracted, from which the system derives, based on a comparison of historical data, an estimation of the vehicles traffic, particularly the number of circulating vehicles and the number of accidents in a unit time.
In EP 763807 a method and system for detecting traffic jams are described; a traffic jam in a certain road section is assessed when the PLMN traffic in the network cell covering that road section exceeds a predetermined threshold. The method also allows determining the driving direction experiencing the traffic jam: assuming that the PLMN traffic threshold is exceeded firstly in a first network cell, and then in the adjacent, second network cell, located for example at the north of the first cell, it can be desumed that the driving direction experiencing the traffic jam is that directed from the north to the south.